The present invention relates to damping the vibrations of at least two stay cables of a civil engineering structure.
By way of non-limitative example, the damping proposed by the invention can in particular serve to damp the vibrations of a stay cable array of a cable-stayed bridge. In cable-stayed bridges, the stay cables forming the stay cable array are generally anchored at their upper end on a pylon and at their lower end on the bridge deck. The stay cable array thus ensures the support and stability of the structure.
However, under certain conditions, in particular when the bridge deck undergoes periodic excitations, the stay cables can build up energy and vibrate significantly. The two main causes of these vibrations are the movement of the stay cable anchors with respect to the deck under the effect of traffic loads, and the effect of the wind acting directly on the stay cables. When uncontrolled, such vibrations are capable of directly damaging the stay cables, while being a source of anxiety to users present on the bridge deck.
In order to avoid or limit the vibrations of the stay cables of a civil engineering structure, it is known to use interconnecting cables that allow for a plurality of stay cables of a single stay cable array to be linked together, the interconnecting cables being moreover directly anchored on the bridge deck. The interconnecting cables allow for the whole stay cable array to be stiffened while allowing for certain, mainly in-plane, vibration modes of said stay cables to be prevented.
However, when interconnecting cables are used for linking together a plurality of stay cables, the following parameters must be taken into account:                the cross-section, rigidity and tension of the interconnecting cables must be determined by an overall calculation of the array of interconnected stay cables;        the strength of the interconnecting cables and of their anchors must be appropriate in extreme load scenarios such as road traffic on the bridge deck or a turbulent wind on the construction or the stay cables;        the pre-tensioning of the interconnecting cables must make it possible to avoid any de-tensioning under extreme load; a de-tensioned interconnecting cable no longer serves its purpose and can undergo shocks that are harmful to the durability of the anchors, which is also likely to lead to a breakage of said interconnecting cable and therefore its replacement by another interconnecting cable having a greater cross-section and rigidity while being tensioned to a higher tension value;        angular fractures of the ends of the stay cables at the level of the anchors must also be assessed, and corrected if necessary.        
Taking into account these different parameters thus complicates to a relatively significant extent the installation of the interconnecting cables in order to stiffen the stay cable array of a civil engineering structure.
Moreover, when such interconnecting cables must be installed after the commissioning of the civil engineering structure, in order for example to correct stability problems, it is essential as described above to pre-tension the set of interconnecting cables, which therefore alters the geometry of the different stay cables of the stay cable array, with consequences for the structure of the construction and in particular the appearance of angular fractures at the level of the ends of the stay cables directly anchored on the pylon and on the bridge deck in the case of cable-stayed bridges.
Another solution consists of using dampers arranged between the stay cables and the structure of the construction or even directly interposed between the stay cables, so as to dissipate a portion of the vibratory energy of the stay cables.
In the interests of efficiency in particular, these dampers are traditionally symmetrical dampers, i.e. they function substantially in the same manner when they are subjected to tensile stress or compressive stress. Typically these are piston dampers having a rectilinear stroke which satisfy a symmetrical and increasing relationship between the force developed and the displacement speed of the piston when they are working under tension (lengthening) or compression (shortening). The symmetry of the relationship is understood from the identical or near-identical behaviour of these dampers under tension and under compression.
However, when operating under compression, the reaction force of the piston can be a source of instability.
By way of example, a stay cable array of a cable-stayed bridge can be considered, in which a respective damper links each pair of adjacent stay cables of the array, the dampers running on from each other. When two dampers on either side of a stay cable are compressed, the stay cable held between these two elements risks being pushed outside the plane of the array.
This instability means that the dampers no longer work.
The present invention makes it possible to limit at least some of the above-mentioned drawbacks.